Method and apparatus for evaluating performance on host data transfer within a tape drive

ABSTRACT

A method for evaluating data transfer performance within a data recording apparatus is disclosed. The data recording apparatus includes a buffer and a recording medium. Initially, a Pause time P when data transfer between the buffer and a host being stopped temporarily is measured. Then, an ideal Pause time Y is determined. Next, a determination is made whether or not the Pause time P exceeds a sum of the ideal Pause time Y and an allowance a. If the Pause time P exceeds a sum of the ideal Pause time Y and the allowance a, a warning signal is sent to the host.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims benefit of priority under 35 U.S.C. §§120, 365 to the previously filed Japanese Patent Application No.JP2006-066625 entitled, “Data Recording Apparatus, and Method ofEvaluating Performance on Host Data Transfer in Data RecordingApparatus” with a priority date of Mar. 10, 2006, which is incorporatedby reference herein.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to tape drives in general, and inparticular to a method and apparatus for evaluating performance on hostdata transfer in tape drives.

2. Description of Related Art

When a tape recording apparatus, such as a tape drive, has been usedover a long period of time, a situation where a processing time forbackup does not end within an expected time period may occur because ofsome reason or another. The overrun of backup time can be attributed tothe degradation in performance on data transfer from a host. In order toprevent the overrun of backup time when the problem is at the driveside, the drive needs to report its problem to the host.

Referring now to the drawings and in particular to FIG. 1, there isdepicted a block diagram of a data recording apparatus system. As shown,a tape drive 100 includes an interface 110, a buffer 120, a recordingchannel 130, a tape 14 a, a head 14 b, reels 14 c and 14 d, a cartridge14 e, a motor 150, a controller 160, a head position control system 170,and a motor driver 185. Interface 110 communicates with a host 105.Interface 110 receives, from host 105, a command for instructing writingof data to be transferred to buffer 120, and a command for instructingwriting of data into buffer 120 and into tape 14 a. Buffer 120 is amemory, such as a random access memory, for saving data to be writteninto tape 14 a.

Data delivered through recording channel 130 are formed in units ofdatasets (for example, 400 KB each), and are written into tape 14 a bymeans of head 14 b. Tape 14 a is wound around reels 14 c and 14 d, andlongitudinally moves along with rotations of the reels in a directionfrom reel 14 c to reel 14 d, or in an opposite direction. Cartridge 14 eis a container for housing reel 14 c around which tape 14 a is wound.Motor 150 rotates reels 14 c and 14 d.

Controller 160 controls tape drive 100. Controller 160 controls thewriting/reading of data into/from tape 14 a in accordance with a commandreceived from host 105 through interface 110. Controller 160 alsocontrols head position control system 170 and motor driver 185. Whenthere is a need for head 14 b to switch tracks, head position controlsystem 170 electrically controls head 14 b so that head 14 b can switchtracks. In addition, controller 160 monitors data (write/read data) ininterface 110, buffer 120 and recording channel 130. Motor driver 185may be connected directly to controller 160.

With reference now to FIG. 2, there is illustrated a process flow afterdata have been received from host 105. In a Linear Tape Open (LTO) typetape drive, for example, after data have been received from a host, datacompression is performed on the fly in interface 110. The host transfersthe data at a maximum transfer rate H (e.g., 160 MB/sec). FIG. 2 showsdata transfer of compressed data from buffer 120 to tape 14 a at a drivetransfer rate T (e.g., 35 MB/sec) by drive 100. Drive 100 performs aWrite action while performing a Pause action for temporarily stoppingtransfer on the host side. During the Write action, the Pause occurswhen a data transfer rate from host 105 to drive 100 is faster than adata transfer rate from drive 100 (buffer 120) to tape 14 a. During aRead action, a Pause state occurs when a host transfer rate from buffer120 to host 105 is faster than a drive transfer rate from tape 14 a todrive 100 (buffer 120). Between host 105 and the drive, data witharbitrary lengths are written or read. Buffer 120 is sectioned intounits of segments of one uniform size for temporarily storing read/writedata. The Pause state occurs during the Write action means that there isno segment in buffer 120 into which subsequent data can be written,i.e., there is no free space in buffer 120. The Pause state occursduring the Read action means that, as data are slow in being read fromtape 14 a to buffer 120, the entire buffer is free space.

Even if data are transferred from host 105 at the rate of 160 MB/sec,when the writing speed (the drive transfer rate) from buffer 120 to tape14 a is 35 MB/sec, host performance is dictated by the drive transferrate as the drive transfer rate is smaller than the host transfer rate.No matter how fast the host transfer rate is, the performance of thehost transfer rate at 160 MB/s cannot be exerted unless the drive canperform writing at a rate of the host transfer rate or higher. Eventhough the host transfer rate is not exerted, if writing data into thetape is performed at a transfer rate close to, or at least, an idealvalue of the drive transfer rate at 35 MB/s, the drive can sufficientlyexert writing performance thereof. Suppose, when the host hastransferred 2:1 compressible data at a rate of 70 MB/s or below, thedata are compressed inside the drive, and therefore, the drivetheoretically never keeps the host side from waiting to transfer. Inother words, the transfer rate H between the host and the drivecoincides with a transfer rate expected by the host. In a case when atime period during which the drive keeps the data transfer from the hostwaiting is close to a calculated value, the drive can be determined assufficiently exerting the drive transfer rate. In this case, even thoughthe host is kept waiting to transfer data to the drive, the degradationin performance is not recognized in the data transfer from the host.

A factor in the performance degradation of the data transfer between thehost and the drive does not necessarily exist only in the drive andcartridge. Also, even if numerous errors have occurred in the tape, itdoes not necessarily lead to the performance degradation. There arevarious factors in such degradation of performance, and it is verydifficult to specify a cause. With respect to a problem concerning theperformance of the tape drive, sometimes the performance degradation wasnot at the drive side but at the user side.

In some cases, the writing of data into tape 14 a from buffer 120 iskept waiting due to some sort of problems in the drive and tape. Thus,the transfer rate H of the host substantially becomes not more than thatrate it should have. When numerous errors occur in the drive, it can beconcluded that the drive itself has become a factor in the performancedegradation of the data transfer from the host. Consequently, it wouldbe desirable to provide a method and apparatus to report to the host anyerror status of the drive before the error become a permanent error(irrecoverable error) when the performance of the drive startsdegrading.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention, adata recording apparatus includes a buffer and a recording medium.Initially, a Pause time P when data transfer between the buffer and ahost being stopped temporarily is measured. Then, an ideal Pause time Yis determined. Next, a determination is made whether or not the Pausetime P exceeds a sum of the ideal Pause time Y and an allowance a. Ifthe Pause time P exceeds a sum of the ideal Pause time Y and theallowance a, a warning signal is sent to the host.

All features and advantages of the present invention will becomeapparent in the following detailed written description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself, as well as a preferred mode of use, furtherobjects, and advantages thereof, will best be understood by reference tothe following detailed description of an illustrative embodiment whenread in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram of a tape drive;

FIG. 2 shows the data flows between a host and a tape drive;

FIG. 3 shows the Pause time values P in relation to calculated values Ywhen there is no problem in a tape drive;

FIG. 4 shows the Pause time values P in relation to the calculatedvalues Y when where there are problems in a tape drive;

FIG. 5 shows control means inside of a tape drive for comparing thePause time P and the calculated value Y;

FIG. 6 is a high-level logic flow diagram of a Host Performance Checkerfor measuring a host transfer rate H;

FIG. 7 is a high-level logic flow diagram of a Pause Time Checker formeasuring a Pause time P during which data transfer from a host is beingkept waiting;

FIG. 8 is a high-level logic flow diagram of a Error Counter forcollecting information on various recoverable errors in an E drive; and

FIG. 9 is a high-level logic flow diagram of a Performance Checker forcomparing an actual measured value P and a calculated value Y.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

With respect to factors in performance degradation in data transfersbetween a host and a drive, the following cases are considered:

I. Causes attributed to the drive side

-   -   A. Causes attributed to the drive itself        -   deterioration in error rate due to degradation in hardware        -   problem in speed setting due to a problem in software    -   B. Causes attributed to a medium        -   deterioration in error rate due to quality of the tape        -   damages on the tape            II. Causes attributed to the usage environment of the drive    -   A. Problem in performance of the server itself    -   B. Problem in performance of the network (including a failure in        a communications network)    -   C. One attributed to an application

For a system operator at the site of the data recording system, it isonly necessary to be able to determine, based on a time period duringwhich the Pause state continues (Pause time), whether the cause existsin the drive and tape, or in some other factor. If the system operatorhas found that the drive side has a problem, the system operator canattempt to improve performance by immediately replacing the drive, thetape cartridge and the like that have the problem. It is only necessaryto be able to take time thereafter to collect error information andanalyze the problematic drive. At the site, it is not necessarilyrequired for the problematic drive to be able to precisely specify thecause of a trouble of the drive by use of the error information that isreported at the same time as the problem occurs.

When there is a problem at the drive side, which affects an actualmeasured value P of the Pause time. For example, when numerous errorsoccur inside a tape drive 100, data write transfer is kept waiting (thePause state) longer than the host anticipates. In such a case, drive 100does not return a Complete signal to host 105 until data saved in buffer120 in the drive are certainly written into the tape. Since host 105cannot send subsequent data until it receives the Complete signal,actual host transfer is delayed. When error processing occurs frequentlyin the drive, the host increases the actual Pause time P during whichthe host stops its data transfer because of the Pause action in thebuffer. As a result, write performance from the host is degraded.Consequently, by measuring the Pause time P in writing data saved inbuffer 120 inside the drive into the tape, it becomes possible todetermine whether or not drive 100 has been a cause of performancedegradation of host 105.

Referring now to FIG. 3, there is illustrated actual measured values Pand calculated values Y (H, T) of the Pause time in cases when there isno trouble in the drive. If a drive transfer rate T (35 MB/s) is largerthan a host transfer rate H (T>H), the calculated value Y of the Pausetime is 0 because it is not necessary to keep the host transfer waiting.When the buffer transfer rate T (for example, 35 MB/s) is smaller thanthe host transfer rate H (T<H), the calculated value Y of the Pause timeacquires a value larger than 0 because it is necessary to keep the hosttransfer waiting. In this respect, when the tape drive has a problem, anactual data transfer rate between the buffer and the tape is larger thanthe ideal value T (for example, 35 MB/s) of the drive transfer ratebecause an error recovery procedure (ERP) mediates therebetween. Theperformance degradation in the host transfer can be evaluated bymeasuring the actual measured value P of the Pause time. When the actualPause time P is larger than the calculated value Y (H, T), the datatransfer from the host is kept waiting, and the performance isconsidered as degraded. Specifically, during the Pause state, data yetto be written into a tape 14 a still remain in buffer 120, and there isno free space available in buffer 120 for accepting the subsequent datafrom the host. Since drive 100 has no free space that can accept data,drive 100 cannot return a Complete signal to the host.

FIG. 4 illustrates a case when host 105 is unable to send data becauseof the Pause action caused by performance degradation. First of all, adetermination procedure of the calculated value Y (H, T) of the Pausetime will be described. When the drive is operating as anticipated, asshown in FIG. 3, the actual measured value P substantially coincideswith the calculated value Y. As a unit in which data are written outonto any one of buffer 120 and tape 14 a, a size D (for example, 400 KB)of a dataset is given. A transfer rate between host 105 and drive 100(buffer 120) is given as the host transfer rate H. A transfer ratebetween buffer 120 and tape 14 a is given as the drive transfer rate T.The calculated value Y (H, T) of the Pause time is a function of thehost transfer rate H and the drive transfer rate T, and the calculatedvalue Y (H, T) is expressed as follows:

If (T >= H) then   Y = 0 else   Y (H, T) = (D/T) − (D/H).

An allowance a is given as an electromechanical margin of the drive, andthe calculated value Y (H, T, a) of the Pause time is given by using thehost transfer rate H and the drive transfer rate T, which are determinedby an electromechanical property of the drive, in the following manner:

If (T >= H) then   Y = a else   Y (H, T, a) = (D/T) − (D/H) + a.

In an actual usage environment, even if there is no problem in the driveside, the actual measured value P of the Pause time never exactlycoincides with the calculated value Y (H, T). It can be presumed that,due to variable factors such as a usage environment of the drive, theactual measured value P becomes more or less larger than the calculatedvalue Y (H, T). If it is allowed for the host side or the drive itselfto arbitrarily set up the allowance a as the margin of the drive, thesystem operator can flexibly maintain an information storage system(such as a tape storage apparatus) depending on the usage environment.For example, when the system operator wants to efficiently realize abackup environment of data in a state where the drive is optimal, thesystem operator can set the allowance a to a small value. But when thesystem operator does not want to frequently replace the drive andcartridge and wants to prolong a maintenance interval to a certainperiod or longer, the system operator can set the allowance a to a largevalue.

When the following formula is satisfied, the drive concludes that thereis a problem in the drive side, and sends a report or a Warning to thehost regarding the reason for the error and a ratio of performancedegradation:

-   -   If (P>Y (H, T, a)) then        -   send Warning.

Because the drive retains various pieces of error information (E), thedrive may report those pieces of error information to the host. ErrorCounter shown in FIG. 5 collects such pieces of error information (E).

FIG. 4 shows the actual measured values P are values Δ when there areproblems in the tape drive, and the actual measured values P are values▴ when there is no problem in the tape drive. When the actual measuredvalues P are values ▴, consider a case when one of the write channelsincluded in the head is not functioning as an example. The actualmeasured values P ▴ and Δ of the Pause time are the same in that theyacquire larger values than the calculated values Y (H, T). The actualmeasured value P of an actual drive acquires, even if the drive is in anideal driving state, a value of the calculated value Y (H, T) or more.If the actual measured values P are simply compared with the calculatedvalues Y (H, T), the values P of all of the drives are evaluated asbeing larger than the values Y (H, T), which does not fit the actualusage status. Thus, when the actual measured values P are included in apredetermined range (the allowance a) using the calculated values Y (H,T) as a reference, it is determined that the drive has no problem.Specifically, the actual measured values ▴ are smaller values than thevalues Y (H, T, a) for which the allowance a is taken intoconsideration, and it is not determined that the drive has a problem. Incontrast, the actual measured values Δ are much larger than the values Y(H, T, a), and it can be concluded that there is a problem inperformance on the drive side.

From the above description on FIG. 4, it can be understand that whetherperformance degradation in the data transfer from the host exists in thedrive side or in the usage environment side other than the drive can bedetermined through comparison of the actual measured value P with thecalculated values Y (H, T) of the Pause time. Whether the cause of theperformance degradation exists in the drive side or in the usageenvironment (examples of which include the host such as a server;hardware setup and a communication line error in a network; and anetwork/an application) other than the drive can be specified, thesystem operator can perform maintenance of the tape drive without makingfutile attempts.

Referring now to FIG. 5, there is illustrated a block diagram of acontrol mechanism of the drive for comparing the actual measured value Pand the calculated value Y (H, T, a) of the Pause time. The controlmechanism may be a part of a program contained in controller 160. Thecontrol mechanism monitors write performance degradation of the tapedrive by measuring the Pause time P inside the drive and the hosttransfer rate H. The drive transfer rate T and the allowance a aredetermined by the electromechanical property of the drive, andtherefore, are not to be measured by the control mechanism of thepresent invention. The control mechanism is functionally classifiedinto: Host Performance Checker (details shown in FIG. 6) for measuringthe host transfer rate H; Pause Time Checker (details shown in FIG. 7)for measuring the actual Pause time P; Error Counter (details shown inFIG. 8) for collecting the error information E; and Performance Checker(details shown in FIG. 9) for calculating the Pause time Y (H, T, a) andcomparing it with the actual measured value P. Parameter Storagerecords: the Pause time P actual measured by Pause Time Checker; thehost transfer rate H actual measured by Host Performance Checker; theerror information E collected by Error Counter; and the like. As shownin FIG. 9, Performance Checker reads the P, H and E from PerformanceStorage, secures the allowance a and the drive transfer rate T, andcalculates the calculated value Y (H, T, a) of the Pause time. Then,Performance Checker compares the calculated value Y (H, T, a) with theactual measured Pause time P, determines whether or not the performancedegradation is in the drive side, and reports a result of the comparisonto the host.

The drive can determine whether the performance degradation in the datatransfer from the host to the drive is inside the drive or in some otherusage environment. The drive can send a result of the determination tothe host, and also transfer thereto the error information E at the sametime. In addition, Performance Checker in FIG. 9 of the drive may onlyhave to transfer the actual measured value P, the calculated value Y (H,T, a) and the error information E to the host. The host side may beconfigured to analyze and determine, based on the information (P, Y andE), that the drive or the tape is a factor in the performancedegradation. In any one of these cases, the system operator of the taperecording apparatus system can determine whether the performancedegradation is in the drive or in the usage environment. When the driveis a factor in the performance degradation, it is possible to have thesystem operator replace a component part, such as a drive and/or acartridge, and complete backup of data within a certain period of time.

With reference now to FIG. 6, there is illustrated a high-level logicflow diagram of a Host Performance Checker for measuring the actual hosttransfer rate H. When drive 100 is not in a Pause state, the measurementof the H is carried out. The Pause state means that drive 100 is unableto return the Complete to the host because writing data inside buffer120 into tape 14 a has not been completed, the buffer has no spaceavailable for saving transfer data. After confirming that the datatransfer from the host has not yet been started (step 600), atransferred data amount and a timer are initialized (step 605). Thetimer is started when the reception of the data transferred from thehost is started in buffer 120 (step 610). With a time period forcarrying out the measurement being sectioned, buffer 120 continuesreceiving data from the host until a predetermined number of units oftime pass (step 615). When that predetermined number of units of timehas passed, the host transfer rate H (for example, 160 MB/s) is computedby dividing a total of the transferred data amount by these units oftime (step 620). The H is used for calculating the calculated value Y(H, T) of the Pause time of the drive. The calculated is H is saved in amemory of the drive (step 625). Taking consideration of variationdependent on the usage environment, the host transfer rate is measuredas needed, and the value is updated (step 625).

Referring now to FIG. 7, there is depicted a high-level logic flowdiagram of a Pause Time Checker for measuring the actual measured valueP of the Pause time. Whether or not the host transfer is being performedis confirmed (step 700) by buffer 120, and, if it is not in a statewhere the host transfer is not being performed, a timer and P areinitialized (step 705), and the buffer receives data form the host (step710). When buffer 120 is filled up with the data, the data transfer fromthe host is stopped because a Complete signal is not returned to thehost (steps 715 and 720). It is not until this point that the timer isset ON, and a measurement of the Pause time is started (step 725). Inbuffer 120, until the Complete is returned (step 735), a time period ofthe Pause state is measured with the timer being in an ON state (step730). When buffer 120 has come to have a space available and become ableto accept data (step 730), controller 160 of drive 100 return theComplete to the host, thereby telling that data transfer is possible(step 735). At this stage, the timer is stopped, and a value of thetimer at this point is recorded as the actual measured value P of thePause time. The actual measured value P is measured as needed to bestored in a memory, and is updated (step 745). In a processing flow inFIG. 9, this actual measured value P is used to compare with thecalculated value Y (H, T, a) (step 750).

With reference now to FIG. 8, there is illustrated a high-level logicflow diagram of an Error Counter for collecting various pieces of theerror information E on the drive, the cartridge, and other parts of thedrive. After confirming that the data transfer is not performed (step800), various error counters are initialized (step 805). When datatransferred from the host are written into the tape by way of buffer 120(step 810), in a case when various recoverable errors had occurred (step815), the error information E on those errors are collected in thememory area (step 820).

Referring now to FIG. 9, there is depicted a high-level logic flowdiagram of a Performance Checker for comparing the actual measured valueP and the calculated value Y (H, T, a) of the Pause time with eachother, and sends a warning to the host that the drive is a factor inperformance degradation. After confirming that the data transfer is notbeing performed (step 900), comparison between the actual measured valueP and the calculated value Y (H, T, a) of the Pause time is started(step 905). As needed, the most updated actual measured value P of thePause time, the host transfer rate H, and the error information E areacquired from the memory area (step 910). Then, the calculated value Y(H, T, a) is found (step 910) by utilizing the drive transfer rate T andthe allowance a that have been already secured. Then, the actualmeasured value P and the calculated value Y (H, T, a) of the Pause timeare compared with each other (step 915). If the actual measured value Pexceeds the calculated value Y (H, T, a), the host is warned that afactor in performance degradation is in the drive (step 925). Upon thereceipt of the warning, the error information may be acquired (step920), and be sent at the same time (step 925). Detailed errorinformation on the drive and the tape may be reported (subjected to“Notify Warning”) to the host. The error information E may be configuredto contain: various reasons for errors and a degradation ratio. Inaddition, the Performance Checker may be configured only to simplyreport the P and Y (H, T, a) to the host, and let the host to concludethat there is a problem in the drive.

In the processing flows shown in FIGS. 5 to 9, a factor in increase inthe actual Pause time P can be specified by analyzing the detailed errorinformation appended upon the receipt of the warning. However, becausethere is a change in external factors such as the host and an extensionof the drive or the buffer, it cannot necessarily be said that anincrease in error (especially, ERP) in the drive and the recordingmedium directly contributes to the Pause time P. An essence of thepresent invention is that, by focusing on the actual measured value P ofthe Pause time being a parameter that directly influences performance,it is only sufficient to determine whether the performance degradationin the host data transfer is in the drive side or in an external factor.In addition, by analyzing the detailed error information, the tape drivesystem of the present invention is able to report, without making vainattempts, through the host to the system operator the necessity ofreplacing constituent parts, including the drive and the cartridge.

As has been described, the present invention provides a method andapparatus for evaluating performance on host data transfer in a tapedrive. Although the present invention has been described with respect toa tape drive, the present invention can also be applied to generalstorage media such as hard disk drives. In addition, although anembodiment related to writing from the host is described, the presentinvention is also applicable to degradation in performance on the hosttransfer upon a data read request from the host.

While the invention has been particularly shown and described withreference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention.

1. A method for evaluating performance on data transfer in a datarecording apparatus, wherein said data recording apparatus includes abuffer and a recording medium, said method comprising: measuring a Pausetime P when data transfer between said buffer and a host is stoppedtemporarily; determining an ideal Pause time Y, wherein said ideal Pausetime Y is determined by Y=D T −D H, where D is a dataset size of a datatransfer, T is a drive transfer rate between said buffer and saidrecording medium, and H is a host transfer rate between said buffer andsaid host; determining whether or not said Pause time P exceeds a sum ofsaid ideal Pause time Y and an allowance a; in response to adetermination that said Pause time P exceeds a sum of said ideal Pausetime Y and said allowance a, sending a warning signal to said host. 2.The method of claim 1, wherein said Pause time P is measured as a timeperiod when no free space exists in a buffer because preceding datatemporarily saved in said buffer have not been written into a recordingmedium of said data recording apparatus, or as a time period whenreading of data into a host is kept waiting because data have not beenread out from said recording medium to said buffer.
 3. The method ofclaim 1, wherein said allowance a is an electromechanical property ofsaid data recording apparatus.
 4. A computer usable medium having acomputer program product for evaluating performance on data transfer ina data recording apparatus, wherein said data recording apparatusincludes a buffer and a recording medium, said computer usable mediumcomprising: program code means for measuring a Pause time P when datatransfer between said buffer and a host is stopped temporarily; programcode means for determining an ideal Pause time Y, wherein said idealPause time Y is determined by Y=D T−D H where D is a dataset size of adata transfer, T is a drive transfer rate between said buffer and saidrecording medium, and H is a host transfer rate between said buffer andsaid host; program code means for determining whether or not said Pausetime P exceeds a sum of said ideal Pause time Y and an allowance a;program code means for, in response to a determination that said Pausetime P exceeds a sum of said ideal Pause time Y and said allowance a,sending a warning signal to said host.
 5. The computer usable medium ofclaim 4, wherein said Pause time P is measured as a time period when nofree space exists in a buffer because preceding data temporarily savedin said buffer have not been written into a recording medium of saiddata recording apparatus, or as a time period when reading of data intoa host is kept waiting because data have not been read out from saidrecording medium to said buffer.
 6. The computer usable medium of claim4, wherein said allowance a is an electromechanical property of saiddata recording apparatus.
 7. A data recording apparatus capable ofevaluating data transfer performance, wherein said data recordingapparatus includes a buffer and a recording medium, said data recordingapparatus comprising: a controller; a pause time checker operational onthe controller for measuring a Pause time P when data transfer betweensaid buffer and a host is stopped temporarily; means on the controllerfor determining an ideal Pause time Y, wherein said ideal Pause time Yis determined by Y=D T−D H where D is a dataset size of a data transfer,T is a drive transfer rate between said buffer and said recordingmedium, and H is a host transfer rate between said buffer and said host;a performance checker operational on the controller for determiningwhether or not said Pause time P exceeds a sum of said ideal Pause timeY and an allowance a; and means on the controller for, in response to adetermination that said Pause time P exceeds a sum of said ideal Pausetime Y and said allowance a, sending a warning signal to said host. 8.The data recording apparatus of claim 7, wherein said Pause time P ismeasured as a time period when no free space exists in a buffer becausepreceding data temporarily saved in said buffer have not been writteninto a recording medium of said data recording apparatus, or as a timeperiod when reading of data into a host is kept waiting because datahave not been read out from said recording medium to said buffer.
 9. Thedata recording apparatus of claim 7, wherein said allowance a is anelectromechanical property of said data recording apparatus.